This invention relates to switches for packet-based data communication networks wherein messages in the form of addressed data packets are conveyed from, for example, user to server and from server to user by way of at least one switch which can respond to address data within a packet to determine an egress port or ports. The invention more particularly relates to the allocation of priority to different classes of traffic.
Data packets of the kind to which the invention relates are intended to conform to the OSI model in that they will normally include source and destination media access control addresses, otherwise known as xe2x80x98layer 2xe2x80x99 addresses in the OSI model, network or protocol addresses of the entities which are communicating, further information, called herein xe2x80x98higher layerxe2x80x99 information identifying for example the xe2x80x98applicationxe2x80x99 which the entities are operating to exchange information, message data and, conventionally, cyclic redundancy code data. As is well known, not all packets will conform to such a format precisely, since the exchange of information between entities, such as a user and a server, may require initially the discovery of appropriate address data by means of an address resolution protocol, but it is assumed in the following that two entities have begun to exchange data using packets conforming to the aforementioned general format.
In order to ameliorate the effects of congestion in networks, it is customary for different types of traffic to be accorded different priority levels. For example, control frames or packets sent by a management entity to a particular designation may be accorded a high priority whereas other traffic may be accorded a low priority. Once a given type of traffic is allocated a particular priority, tile priority may be indicated and implemented in a variety of ways. Which of these is selected is not important to the present invention. Some ways of implementing it will be discussed in relation to a specific example.
For a variety of different applications, for example those relating to HTTP (hypertext transmission protocol) the bandwidth requirement for traffic from the server to the xe2x80x98clientxe2x80x99 far exceeds the requirement for bandwidth from the xe2x80x98clientxe2x80x99 to the server. Typically the ratio of the requirements for bandwidth is 5 to 1 or greater. Where conversations (the exchange of messages) are allocated the same priority in both directions there is a substantial waste of the bandwidth allocated to the messages passing from client to server.
The present invention is based on the detection of the commencement of a conversation by recourse to higher layer information, that is to say layer 4 or above, to provide storage of the source port associated with the message and to allocate traffic which passes through the switch with a destination port equal to the stored or latched source port a higher priority. That technique will allow server-client traffic to have a higher priority than client server traffic and avoid the wastage of bandwidth noted above.
Further features and benefits of the present invention will become apparent during the following detailed description with reference to the accompanying drawings.